This invention relates to the structure and operation of communication modules which have two control ports that are coupled to respective computers, and one communications port that is coupled to a communications channel.
With such a communications module, each of the computers can send an intra-processor command to a respective control port which initiates some action in the communication module that directly effects the computer which sent the intra-processor command. Also, each of the computers can send an inter-processor command to a respective control port which initiates some action in the communication module that directly affects the other computer which did not send the command.
For example, one intra-processor command can initiate the passage of data from the communications channel through the module to the computer which sent the command. By comparison, an inter-processor command to the communication module can stop the passage of data between the communications channel and the computer which did not send the command.
Since an inter-processor command from one processor directly affects the other processor, it is very desirable to have some sort of security built into the communications module whereby any erroneously generated inter-processor commands are detected and the corresponding operations are inhibited from being carried out. Otherwise, if a processor has a certain fault which causes it to erroneously send bogus inter-processor commands, the effect on the other processor can be disastrous.
Accordingly, a primary object of the invention is to provide a three port communications module which is immune from inter-processor commands that are sent due to certain types of faults.